Liquid organic nitric esters which have been tested for possible use as plasticizers for nitrocellulose include glycerol trinitrate, glycol dinitrate diethylene glycol dinitrate, triethyleneglycol dinitrate (TEGDN), 1,2,4-butanetriol trinitrate (BTTN), and 1,2,6-hexanetriol trinitrate. While all of these, and other similar materials, may be used as energetic plasticizers for nitrocellulose under varying conditions, all suffer from various drawbacks such as high sensitivity, headache inducing properties, low power and/or brisance, poor colloiding activity, etc. Trimethylolethane trinitrate (TMETN), because of its relatively low sensitivity, its high explosive power, and its lack of headache inducing properites is a desirable plasticizer for use in the preparation of flexible explosive compositions containing essentially 100% active ingredients, but its lack of colloiding power has largely discouraged its practical use as a plasticizer for nitrocellulose in the past. Upon contact with ordinary low viscosity nitrocellulose, TMETN softens the surfaces of the nitrocellulose fibers but is incapable of achieving penetration and complete colloidation of such nitrocellulose and hence is considered unsuitable for the preparation of single and multiple base propellants. The high viscosity, high molecular weight nitrocellulose required for use in the present invention is even less affected by TMETN, although it has been found in the course of the development of this invention that long term milling may be used to accomplish such colloiding action. As noted in U.S. Pat. No. 3,400,025, the difficulty experienced in colloiding nitrocellulose with TMETN may be partially overcome by employing TMETN in combination with a substantial proportion of an inert plasticizer, such as acetyl tributyl citrate, and carrying out the colloiding procedure in the presence of a volatile colloiding agent, such as butyl or ethyl acetate or acetone, which is later driven off leaving the nitrocellulose completely colloided with the mixture of TMETN and inert non-volatile plasticizer. Attempts to extend this process to the preparation of flexible explosive compositions containing a nitrocellulose/TMETN binder system which did not contain acetyle tributyl citrate, or similar supplementary inert plasticizer, resulted in the formation of rather hard compositions having little or no flexibility and poor flexure strength.
Further, in previous work on flexible sheet explosives disclosed in U.S. Pat. Nos. 3,317,361, 3,354,010 and 3,400,025, it has been found that low viscosity nitrocellulose could not be substituted for high viscosity nitrocellulose in the binder system when an inert (non-explosive) ester, or a mixture of a liquid organic nitric acid ester and an inert ester was used as plasticizer. In preliminary experimental work connected with perfection of this invention, 37 batches of material were prepared wherein TMETN or TEGDN was used as the plasticizer and various propellant and lacquer grade nitrocelluloses containing 12-13% nitrogen and ranging in viscosity from about 1/2 to 18 seconds were used alone and in conjunction with high viscosity nitrocellulose. It was found that the low viscosity nitrocelluloses were not suitable replacements for high viscosity nitrocellulose. As increasing proportions of high viscosity nitrocellulose were substituted with low viscosity nitrocellulose, the strength of the processed flexible composition decreased until at complete substitution of high viscosity nitrocellose in the binder, the product became too weak to serve any useful role as a sheet explosive.